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Can metals be compressed? I've noticed that a metal coin

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Can metals be compressed? I've noticed that a metal coin can remain intact with distinguishable features for centuries even in wet environments but some metal things rust away very quickly.

I watched a video of how the US Mint made quarters and the sheets of metal they used looked pretty flimsy and flappy but after being put under a ten ton press those quarters are solid as fuck.


Does compression change metal significantly? Does it actually compress or do the forces just alter the metal?

I have asked a few questions here about smithing and such and you guys always have great responses.


What point would there be to compression anyways?
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I know gold and silver coins can be intact and keep distinguishable features for thousands of years... because gold and silver don't really rust or corrode.

But I think I've noticed metal coins resist corrosion much better than other things.

It might be all in my head.
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>>881486
Nah, you can't compress solid metal. The main reason those coins seem stiffer than the sheets they are punched from is because they are a lot shorter. The extra length acts like a level and makes it easier to bend them. Shorten them up and they before harder to bend.
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>>881491
>level
*lever. Derp.
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>>881491
This.

But OP should know that forging does make metal stronger. I don't completely remember why, but it has to do with beating the crystals or molecules in the same direction.

Its why forged parts (beaten into shape) are stronger than cast or milled.
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>>881486
>Can metals be compressed?

Of course they can, they're just highly incomprehensible, and at even thousands of psi they don't compress very much. When the shape charges in a nuclear bomb go off they compress the plutonium at the center to a fraction of its uncompressed size.

Most metals also contain microscopic bubbles that form when dissolved gas comes out of solution when they're cooling from liquid to solid. This is why forged metal items (being shaped by hammering or pressing) are often stronger; the compression of the hammer squeezes these bubbles closed, which increases the density and therefore strength of the metal.

>I've noticed that a metal coin can remain intact with distinguishable features for centuries even in wet environments but some metal things rust away very quickly.

Some alloys have much higher corrosion resistance than other alloys that are very, very similar.
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You cannot compress a metal, you wold just cause distortion, however for a stronger metal they use different techniques, ie: pig iron is made in a blast furnace, and most high quality Metal (semi killed and killed) are made using other methods (electric arc furnace) it's really all in the amount of garbage you have in it, more oxygen and other impurities makes the metal worse, (rimmed steels) and when you take out impurities you get higher grades...I'm actually pretty curious as to which the mint uses
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Pure metallic elements naturally form crystalline lattices, which cannot be compressed. Stamping a coin merely deforms the metal, rather than compressing it. Its mass and volume remain the same.

The persistence of a coin's features over time has to do with the metal's resistance to oxygen. If all oxygen-exposed atoms of the metal are positively charged, then they will quickly join with oxygen atoms and form metallic oxides, which you know as rust. In some cases, the metallic object rusts down to nothing, but others (like aluminum or 300-series stainless) form a protective crystalline layer of oxides which actually protect the core metal from further oxidation.

An dat be how it do. Mmhm.
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>>881486
It's called work hardening.
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literally everything can be compressed. supposedly our entire universe was at some point compressed into something the size of an atom or some bull shit. suns are also made of lots of highly compressed shit and the theory is that black holes massively compress everything they suck in
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>>881486
1) metals chosen for coins are picked for their resistance to corrosion and wear.
2) when a coin becomes notably worn (at least in modern terms) it is retired from circulation, creating an artificial scarcity of worn/damaged/corroded coins.
3) the sheet material only seems to change. You would notice the same effect when dealing with a piece that size stamped or cut from sheet metal.
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One of my professors had this slug of highly compressed metal, was going to analyze it at a synchrotron light source. I forget how it got compressed.
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>>881531

Compressing a structure/gas/whatever is not even close to the same as actually compressing matter.

Actually increasing the density of an already solid (or even liquid), otherwise incompressible object requires pressures that earth has only ever seen in particle accelerators. For all practical purposes, it's outright impossible.
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>can metals be compressed

Simple answer, no

Complicated answer, yes

>why do some metals rust away and others don't

It has to do with two things. How reactive is the pure metal with oxygen and if the oxide layer is protective.

Gold is pretty much inert. It will not corrode under normal circumstances. Aluminum on the other hand is highly reactive with oxygen, but the oxide layer is protective. When you look at aluminum you are actually looking at an extremely thin layer of oxide. Iron is also reactive with oxygen, but it's oxide is not protective. Look up Pilings Bedsworth Ratio to learn more about oxide layer formation.

>why is the stamped metal stronger than the sheet

That has to do with something called strain hardening. When metal is deformed it produces dislocations. Dislocations are crystal defects in the lattice. The more dislocations there are the harder it is to produce more dislocations, and subsequently deform the metal. Look up the relation between dislocation density and stage 3 work hardening (cross slip).

So the answer to most of your questions can be summed up by reading a god damn book.
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>>881486
>I watched a video of how the US Mint made quarters and the sheets of metal they used looked pretty flimsy and flappy but after being put under a ten ton press those quarters are solid as fuck.
>under a ten ton press
the machines for doing this stuff are called "coining presses".
They ARE a big hydraulic press with dies in it, but they are a particular type of industrial press and usually with capacities WAY more than ten tons.

200 to 300 tons is a typical size for making smaller coins out of relatively soft metals.
I dunno what they're using now, but for many years the ones that the US mint used to make quarters were 650-ton capacity.

pic semi-related: a mashed penny I found laying near some railroad tracks... why one side is blank and the other side isn't, I have no idea
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I love these kinds of threads. Just reading all the comments from uneducated imbeciles makes my day. There are only ever 2 or 3 people that have a clue. The rest have no clue what they are talking about, but that doesn't stop them from posting.
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>>881531
This is based on forces powerful enough to compress the fabric of space, as in the volume of a given area of space, even in a vacuum. in other words technically yes you could compress a cube of metal, but not by increasing it's density but by compressing the literal space the cube occupies and thusly the cube by association. I don't think that is the kind of compression OP was talking about...
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>>883044
Don't forget the idiot that has nothing to contribute.
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>>881486
Hi friend, Materials Engineer here. Basically listen to this guy >>881723
You can also change the density of your metal by inducing a phase change, for example austenitic steels have different densities than martensitic steels. These different phases are usually achieved through a combination of playing with alloying elements, heating and cooling processes that affect how much time the crystalline structure has to form, or mechanical forces exerted on the material.

The first book you'll want is probably going to be Materials Science and Engineering by Callister which I'm sure is available for torrent wherever you look.
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>>883086
Continued because I'm bored.

Basically depending on the phase of your solid, you can have different crystalline structures, so your atoms are oriented in different repeating patterns, which result in different densities. Most basic of which are FCC (Face Center Cubic) and BCC (Body Center Cubic) lattices. Atoms in the FCC pattern are packed tighter than BCC. You can calculate it roughly but it's pretty obviously different in the image.
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>>881522
annealing
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>>881545
>Compressing a structure/gas/whatever is not even close to the same as actually compressing matter.

why dont you stop posting for a while there, ace.
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>>881497
the plutonium is kept in an "uncompressed" way with air or other material in between so it does not reach critical mass. there is no solid mass being compressed
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>>883054
Like you ?
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>>881531

Not really the same thing, but you're right. It's theoretically possible to compress anything, and stuff gets weirder and weirder as you go.

First off, you're talking about the conditions that existed at the big bang and the origin of the universe. All matter was highly compressed, but it was only compressed because the universe was literally small. OP is talking about actually forcing matter together.

Compressive states of matter, from low to high:

Vacuum (no matter)
Ordinary matter (complex molecules can form)
Crystalline matter (found at pressure and temperature inside planets, can be man-made)
Dense plasmas (atoms loose their electrons, atmosphere of the sun)
Fusion occurs (stellar fusion - larger and hotter stars can fuse anything up to iron)
Nova and supernova fusion (all elements heavier than iron originate in nova/supernova fusion)
Neutron stars (repulsive force between protons and electrons is overcome)
Black holes (infinitely dense matter)
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>>881491
Technically, it doesnt become harder to bend after cutting them from the sheet.

"Bendiness" remains the same.

What does change is the angle/length of moment/movement changes.

Think Lever.

The further you are from a point, the lower the energy required at that point to lift an object. This object doesnt weigh less, it just becomes easier to lift.

Sorry, woke up in an anally-retentive mood.
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>>884082
>Technically, it doesnt become harder to bend after cutting them from the sheet.

Wrong

See

>>881723

Strain hardening is real my friend
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http://hackaday.com/2012/09/28/how-a-quarter-shrinker-works/
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>>885053
I wanted to post this since someone posted you can't compress shit, but I couldn't be bothered.
http://teslamania.delete.org/frames/shrinkergallery.html
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>>885060
Hey, dumbass, read the fucking site before you post stupid shit.

>The coin also becomes thicker as it shrinks in diameter. Despite the radical changes to the coin, its mass, volume, and density all remain the same before and after shrinking.
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>>885060
You're an idiot.
http://teslamania.delete.org/frames/shrinker.html
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>>885088
its obviously the same thickness
Thread posts: 32
Thread images: 5


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